The serrated yielding in metals and alloys is an important and interesting physical phenomenon. No. 3004 aluminum alloy has been subjected to tension test in a range of strain rates 5.56×10-5s-1—5.56×10-3s-1 and temperatures 223K—773K to investigate the ordinary rules of serrated yielding phenomenon. The micro-mechanism and physical essence of serrated yielding of the material has been studied by means of activation energy, internal friction and microstructure. The results show that the serrated yielding phenomenon is associated with the dynamic strain aging process. In the serrated yielding temperature region, an anomalous serrated yielding phenomenon was found. Within this temperature region, a critical transition temperature Tt exists. The critical plastic strain for the onset of serrations has a negative or positive temperature coefficient within the temperature region lower or higher than Tt, respectively. The former is the normal serrated yielding and the latter is called “anomalous”. It is believed that the process at the temperature region lower than Tt is controlled by the interaction between Mg solute atom atmosphere and dislocations. In the positive coefficient region, the aggregation of Mg atoms and precipitation of second phase decrease the effective amount of Mg atoms in solid solution and leads to the appearance of a positive temperature coefficient of the critical plastic strain for the onset of serrations.